This invention relates to a wastewater treatment system and more particularly it relates to a shipboard wastewater treatment system where the system operates in the extreme from very high loading to very low or no loading and may remain in a dormant state for periods of time. Also, the system is useful for treating bilge water.
Treatment of black water (sewage) and gray water (wastewater from showers, sinks, kitchens, etc.) aboard ships has many problems when compared to land-based facilities. For example, onboard ship, low flush vacuum toilets are used for conveying black water and thus there is a lack of water dilution because of the low flush and also because of the absence of surface run-off to dilute the organic load. Further, a variety of devices may be used on board ship to restrict the quantity of gray and black water. All of these considerations result in a wastewater which has an average strength much greater than domestic sewage and a quantity per capita per day which is much lower.
Another problem with onboard ship treatment of wastewater results from the short time between human activity, resulting in waste generation, and arrival of waste at the treatment plant. This results in sharp diurnal variations in waste generation onboard ship in which peak waste quantity and quality tend to coincide rather than being separated as on land. For example, onboard ship, nighttime flow rates may be only one tenth ({fraction (1/10)}) or 10% of the average daytime flow rate, resulting in further problems for a treatment facility.
In addition, onboard ship treatment facilities have a problem with the space that can be dedicated to waste treatment. For example, the height between decks is limited to 8 feet or less, thus standard items for land use facilities cannot be used. Further, ship motion greatly reduces from consideration other standard features, and the lack of trained waste treatment personnel on board requires a very reliable system which is substantially fully automated.
Also, it is important that a system used for black water or gray water be capable of treating bilge water containing oily substances, for example, petroleum and biodegradable material. Thus, by the term wastewater as used herein is meant to include bilge water.
Thus, it will be seen that there is a great need for a shipboard or compact waste treatment system which will overcome these problems and which can be fully automated for shipboard use. Further, the shipboard system must be capable of periods of standby or inactivity, for example, when the ship is in port and yet, be capable of reaching full capacity within a few hours, when the ship is fully loaded with personnel.
Different systems have been proposed for treatment on onboard ship systems. For example, U.S. Pat. No. 5,807,485 discloses an apparatus and method for the continuous biological treatment of ship bilge water contaminated with petroleum and biodegradable materials. The apparatus includes a pumping system attached directly to the bilge or to an oil-water phase separator, for removing the biodegradable material(s) contained in the bilge waste aqueous phase, which is integrated with a means for microbiologically treating the contaminated bilge water. The means for microbiologically treating the contaminated bilge water preferably includes petroleum- and hazardous-degrading microorganisms. In operation, a phase separator system on the ship separates the free-product phase from the contaminated bilge water. The separated free-product is removed for off-site disposal. Contaminated bilge water is fed into the microbiological treatment system for further treatment with eventual discharge overboard or recirculation into the contaminated bilge area.
U.S. Pat. No. 5,151,187 discloses a system for biodegrading oxidizable organic waste in a bioreactor in combination with a membrane ultrafiltration unit used to separate a high quality permeate from activated sludge which is returned to the bioreactor from the membrane unit as a recycle stream. It has been found that in-line fine bubble diffuser or xe2x80x9cmicronizerxe2x80x9d takes advantage of the kinetic energy in the recycle stream to aerate the biomass with surprising efficiency. The micronizer is positioned external to the biomass in the bioreactor; the discharge from the micronizer provides a microaerated tail-jet of the recycle stream which has been infused with a mass of air bubbles from 1-1000 xcexcm in diameter. The velocity of the compressed air flowed into the micronizer keeps its pores from clogging with sludge. The energy of the recycle stream without the air is insufficient to provide the requisite motive force for adequate oxygen transfer and to establish a predetermined recirculation pattern.
U.S. Pat. No. 5,248,424 discloses a membrane device for withdrawing permeate from a substrate, the flux through the membranes reaching an essentially constant relatively high value because of the critical deployment of fibers of the array as a skein, arching in a buoyantly swayable generally parabolic configuration within the substrate, above at least one of the array""s headers in which the terminal end portions of the fibers are potted. The length of each fiber must be greater than the direct center-to-center distance between the array""s pair of headers. For use in a large reservoir, an assembly of the array and a gas distributor means has fibers preferably  greater than 0.5 meter long, which together provide a surface area  greater than 10 m2. The terminal end portions of fibers in each header are substantially free from fiber-to-fiber contact.
U.S. Pat. No. 3,472,765 discloses techniques of carrying out biological reactions in conjunction with selectively pressure driven permeable membranes to effect high rate separation of biological life from a carrier liquid or a valuable product of the reaction.
U.S. Pat. No. 4,749,494 discloses an activated sludge treatment process for waste water. In the waste water treatment, waste water containing organic matter is introduced into an activated sludge reaction tank. The excess sludge formed in the reaction tank is introduced into a sludge digestion tank to effect the digestion of said excess sludge by intermittent aeration with air. A part of the digestion tank liquid is passed through a filtration apparatus having an ultrafiltration membrane. The filtrate passed therethrough is withdrawn outside the system and the remainder is circulated to the digestion tank to maintain the liquid volume of the digestion tank at a definite level. When the amount of the reaction tank liquid introduced from the reaction tank into the digestion tank is taken as W1, the digestion tank liquid is returned in an amount of (0.2-0.8) W1 to the reaction tank. Thus, the amount of excess sludge to be treated outside the system can be reduced or can be completely eliminated.
U.S. Pat. No. 5,254,253 discloses a system for treating oil water or bilge water in addition to treatment of black water and gray water. The combination provided the essential nutrients for a mass of mixed microorganisms which are well adapted to ingest the nutrients. To facilitate availability of oxygen to the microorganisms so as to provide growth of the microorganisms, and also, to allow them to destroy themselves, excess oxygen is discharged, in a combination of microbubbles and macrobubbles, into a membrane bioreactor (MBR). The mixture of bubbles is preferably generated with coarse ( greater than 2 mm) and fine ( less than 20 xcexcm) bubble diffusers. An auxiliary stream, whether alone or a recirculating stream into which air is drawn, may provide the coarse bubbles. The air is entrained in a jet aerator or eductor in a recirculating loop of activated sludge taken from the MBR. Another portion of the contents of the MBR is pumped to a semipermeable membrane which provides water (permeate) of excellent quality. The remaining concentrate is led to a gas micronizing means which produces a tail-jet of microaerated concentrate. The tail-jet is returned to the MBR to provide kinetic energy for maintaining a high velocity of liquid flow in the MBR. A portion of the concentrate is disposed of. Preferably, the liquid waste to be treated onboard does not substantially exceed about 21 meters3/day.
U.S. Pat. No. 4,071,445 discloses a method of treating wastewater on a ship comprising the steps of passing wastewater through a coarse mesh filter and a crushing means; causing the filtered wastewater to flow upward; passing the wastewater through a plurality of downwardly slanting open cellular plate-like members projecting alternately from a pair of opposed walls defining a passage for the upward flow of the wastewater, with a small space provided between the free end of each of the plate-like members and the wall opposed thereto, while causing large suspended solids to be separated from the wastewater and accumulated in a concentrated state beneath each of the plate-like members by flotation with bubbles generated in the interior of each of the plate-like members to thereby reduce suspended solids in the waste water to below 1,000 ppm and clarifying the resulting treated water by passing the treated water through a semipermeable membrane.
U.S. Pat. No. 4,197,200 discloses an automatic dual-mode shipboard wastewater treatment system employing ozone for disinfection of the primary effluent. Solids are removed and pumped, for example, to the ship""s boiler or other equipment for incineration, while the liquid waste is pumped through a series of ozone reactors and then to a holding tank from which it is discharged overboard, after accumulating to a predetermined level. The system operates continuously by recirculating the effluent, during low flow periods, between a second holding tank and the ozone reactors.
U.S. Pat. No. 4,268,389 discloses a sewage treatment device of the marine type and operates on an extended aeration principle employing an aerator, clarifier and disinfector. The clarifier is disposed beneath the aerator and the top of the clarifier with a common wall therebetween which forms the bottom of the aerator. A first passage conducts fluid from the aerator to the clarifier and has a central port in the common wall. A second passage conducts fluid from the clarifier to the disinfector. The aerator has an influent inlet and the disinfector has an effluent outlet. The treator includes in the aerator vessel nozzle means for admitting air to the vessel in a direction to cause fluid in the vessel to move orbitally about a vertical axis with the nozzle means being disposed at a level proximate the common wall between the aerator and clarifier.
U.S. Pat. No. 5,759,491 discloses a process and apparatus for the decontamination of infectious waste which produces a flowable influent slurry from a solid waste and aqueous liquid. The influent slurry is caused to flow through a conduit which includes a heat exchanger, a heater which brings the temperature of the slurry to at least 125xc2x0 C., and a convoluted holding zone which provides a residence time of at least 15 minutes for the heated slurry. In-line agitation of the slurry is accomplished by injection of pressurized gas.
U.S. Pat. No. 5,785,865 discloses a wastewater treatment system for wharf-mooring or riding-at-anchor vessels, boats, ships and watercraft in general, comprising a number of tanks adapted to be submerged and each provided with a respective drawing tube having a connector plug for watertight connection to a wastewater outlet of a respective boat or the like. The tanks are connected to a self-contained purification installation for intaking and treating the sewage.
U.S. Pat. No. 5,658,458 discloses a recycling apparatus for use in a closed-loop waste treatment system which includes components for removal of inert materials. Typically, the system includes a treatment vessel used in conjunction with a clarifier in an internal recycle configuration; clear water from the top of the clarifier is conducted away from the system as treated effluent, while a portion of the biomass settling at the bottom of the clarifier is returned to the head of the treatment vessel through a hydrocyclone and screen arrangement to remove inert content, thereby substantially increasing the efficiency of biological waste-digestion processes.
In spite of these disclosures, there is still a great need for a shipboard waste treatment system which overcomes the problems enumerated above. The present invention provides such a system.
It is an object of this invention to provide an on shipboard biological wastewater treatment system.
It is another object of this invention to provide an on shipboard wastewater treatment system using submerged membrane microfiltration or ultrafiltration.
Yet, it is another object of this invention to provide an on shipboard wastewater treatment system utilizing an activated sludge process and submerged membrane microfiltration or ultrafiltration in combination capable of high peak loading and capable of being maintained on a stand-by mode.
Further, it is another object of the invention to provide an on shipboard waste treatment system utilizing an activated sludge process and microfiltration membrane combination capable of high peak loading and the microorganism capable of activation in a few hours as the ship leaves port.
And further, it is another object of the invention to provide an on shipboard waste treatment system employing activated sludge and filtration membrane with an improved process for removing insolubles such as cloth, paper, plastic, hair and fibers which detrimentally interfere with membrane operation.
These and other objects will become apparent from a reading of the specification and claims appended hereto.
In accordance with these objects, there is provided a method and system for treating wastewater in an onboard ship sewage treatment system having controlled mixed liquor suspended solids (MLSS), the method comprising the steps of collecting wastewater in a collection tank and transferring the wastewater to a bioreactor to oxidize organic material contained in the wastewater by adding oxygen-containing gas thereto. The bioreactor is operated to provide a mixed liquor having a suspended solids concentration of at least 5 g/l and the mixed liquor solids concentration is continuously increased in the mixed liquor in the bioreactor to not greater than 30 g/l. When the solids concentration in the mixed liquor reaches at least 15 g/l, a portion of the mixed liquor solids is removed from the bioreactor. Thereafter, wastewater is added to the bioreactor to decrease the solids concentration of remaining or residual mixed liquor to not less than 5 g/l. The bioreactor is further operated to increase the solids content again. A hollow fiber membrane container is provided in liquid communication with the bioreactor. The hollow fiber membranes may be disposed substantially horizontally or vertically in the membrane container. A gas dispersing means is located in the container beneath the hollow fiber membrane for sweeping the hollow fibers with gas bubbles. A flow of mixed liquor is directed from the bioreactor to the container to cover the membranes to avoid substantial exposure of the hollow fibers membranes during motion of the ship. Concentrate and mixed liquor are returned from the hollow fiber membrane container to the bioreactor and purified water is removed from the mixed liquor through the hollow fiber membranes as permeate to provide treated effluent.